It is a general tendency that the performance, availability, and reliability of networks based on the internet protocol, so-called internet protocol (IP) networks, is increasing. Similarly, telephone switched circuit networks (TSCN) have been developed and improved for many decades and telephone switched circuit networks work very reliably. Telephone switched circuit networks are commonly used to interconnect mobile and fixed telephones. As the number of users and their respective bandwidth requirements increase, it becomes necessary to increase the capability of telephone switched circuit networks. Expanding and maintaining telephone switched circuit networks requires however massive investments which could be saved to some extend if telephone services could be provided by IP networks. Telephone switched circuit network carriers are therefore willing to consolidate both, IP networks and telephone switched circuit networks.
In a telephone switched circuit network two types of data traffic are used: media data traffic and signalling data traffic. Both types of data traffic can be migrated separately from telephone switched circuit networks to IP networks because they rely on different technologies.
In most public telephone switched circuit networks the signalling data traffic is carried in a packet network which is referred to as Signalling System 7 network (SS7 network). The Internet Engineering Task Force (IETF) has initiated the SIGTRAN working group which defined open standards for transporting SS7 signalling data traffic over IP networks. The architecture that has been defined by the SIGTRAN working group consists of three components: a standard internet protocol, a common signalling transport protocol that supports a common set of reliable transport functions for signalling transport which is referred to as stream control transport protocol (SCTP), and an adaptation sub-layer that supports specific primitives, such as management indications that are required by a particular signalling application protocol.
One new adaptation sub-layer amongst others is the Signalling Connection Control Part (SCCP) user adaptation layer which is abbreviated as SUA layer. On the SUA layer a protocol is defined for the transport of any SCCP user signalling on the IP network. This protocol is called SUA protocol and defined by IETF.
For this protocol the IETF has defined two main entities, a signalling gateway and a SUA application server. The signalling gateway interconnects a SS7 network and an IP network. One or more SUA application servers are located on the IP network which can be requested by a SCCP user signalling on the SS7 network by via the signalling gateway. Alternatively, a SUA application server on the IP network can request a SCCP user signalling on the SS7 network by use of the signalling gateway. A SCCP user signalling is also referred to as SCCP service and a SUA application server is also referred to as application server.
A SCCP service in the SS7 network is declared by use of a point code (PC) and a subsystem number (SSN). On the SUA layer, an application server can be declared by a lot of characteristics, for example by a point code, a subsystem number, a global title (GT), a calling party address, or a mobile application part (MAP) parameter.
When a SCCP data message is received from a node of the SS7 network at the signalling gateway, the point code, subsystem number, and other parameters are extracted from the SCCP data message and a pattern matching is carried out on the SUA layer. From the pattern matching it is determined to which application server the SCCP message is routed to. The SUA routing mechanism is based on user defined matching rules. These matching rules are referred to as routing key rules and the routing key rules are comprised in a routing key file on the signalling gateway.
A SS7 node can send a subsystem test (SST) SCCP management message to the signalling gateway in order to request the availability of a service which is dispatched into one application server on the internet network. In response to a SST SCCP management message the signalling gateway sends a subsystem allowed (SSA) or a subsystem prohibited (SSP) SCCP management message depending on the status of the application server. A SSA SCCP message specifies the availability of an application server and a SSP management message specifies the unavailability of the application server.
Additionally the signalling gateway can inform a node by a SSP or a SSA SCCP management message that the status of the application server has changed.
However, a SCCP service on the SS7 network can be dispatched into several application servers on the internet network, whereof some might be available and some might be unavailable. For such complex scenarios, no satisfactory solution is available that allows for the determination of a control message which is to be sent in response to a SST SCCP management message or in response to a change of an application server status. An improved method and system of coupling a telephone switched circuit network to an internet protocol network is thus desirable.